The number of people who depend upon a wheelchair for mobility increases as medical science continues to progress in the treatment of the elderly and disabled. Advances in the areas of wheelchair design and light-weight materials allow users to remain more active and to participate in more activities than in the past.
In addition to the dimensions and the weight of a wheelchair, there are a wide range of factors that are considered in designing wheelchairs and in the selection of a particular wheelchair by a disabled person. Perhaps the most obvious factor is the means for allowing a user to propel the wheelchair. The most common design is pushrim propulsion in which the user applies force to pushrims that are attached adjacent to the two main wheels. A concern with the use of pushrim propulsion is that the human body is not biomechanically suited for pushrim propulsion, so that inefficiencies, pain and sometimes injury result. Users of pushrim manual wheelchairs may suffer from Repetitive Strain Injuries (RSI) of the wrists and shoulders. The shortcomings of pushrim wheelchairs cause many users to turn to electrically powered wheelchairs. However, such wheelchairs are expensive and more difficult to transport. An alternative which addresses the concerns of pushrim and motor propulsion is the use of levers which allow the user to apply force by a “rowing” action.
Regardless of the selection of the means of propulsion, there are a number of design factors which may be considered to be “user interface” considerations. U.S. Pat. No. 4,560,181 to Herron describes a lever propulsion wheelchair that includes finger-controlled hand brakes similar to those common to bicycles. A hand brake is sufficiently close to a hand grip that a user is able to apply pressure to the hand brake while remaining in contact with the hand grip. A less complex braking arrangement is described in U.S. Patent Publication No. 2007/0024021 to Rand et al. Rather than a number of interacting components, Rand et al. connects a friction element directly on the lever and in alignment with the pushrim, such that an applied force which causes the lever to bend will cause contact between the friction element and pushrim, thereby slowing the wheelchair.
U.S. Pat. Nos. 5,263,729, 6,007,082 and 6,893,035 to Watwood et al. also describe lever propulsion wheelchairs having user-interface features on the levers. Shifting from a forward direction to a rearward direction may be accomplished by manipulating a shift paddle that projects radially from the hand grip end of a lever. A cable couples the paddle to a transmission that permits the lever drive to provide either forward or rearward propulsion. For the convenience and comfort of the user, the handle can be rotated from a position aligned with the lever to a position perpendicular to the lever. As a separate consideration, brake pads may be formed on the levers adjacent to the rims of the wheels, so that outward pressure on the levers causes the brake pads to contact the wheel rims.
Another patent of interest is U.S. Pat. No. 5,020,815 to Harris et al. The wheelchair described in Harris et al. includes a forward/reverse control lever projecting outwardly from the handle of a drive lever. Additionally, rotation of the levers causes steering of the wheelchair by linking the levers to caster wheels that are common to wheelchairs.
While prior art approaches for providing wheelchair propulsion and other motion control features operate well for their intended purposes, further advancements are sought. Of particular concern is the design of a wheelchair motion control system that is well suited for persons who are able to utilize lever propulsion, but who have dexterity difficulties. Ergonomic and easily accessible and manipulable controls increase the range of available activities and facilities for wheelchair-confined persons.